Drinking Water Standards 

& Health Effects

Drinking water standards are set by the U.S. 

Environmental Protection Agency (US EPA) to control 

the level of contaminants in the nation’s drinking 

water. The Safe 

Drinking Water Act 

(SDWA) requires US EPA 

to set these standards, 

which public water 

systems in the U.S. are 

required to meet. US 

EPA has set standards 

for 90 chemical, 

microbiological, 

radiological, and 

physical contaminants 

in drinking water. US 

EPA and others are 

currently conducting 

research and 

collecting information 

to determine which 

currently unregulated 

contaminants pose the 

greatest public health 

risk and will therefore 

be regulated in the 

future.

US EPA also sets 

Secondary Drinking 

Water Regulations, 

which are nonenforceable guidelines 

for contaminants that 

may cause cosmetic 

effects (such as skin 

and tooth discoloration) 

or aesthetic effects 

(such as taste or odor). 

Water systems are not required by US EPA to adopt 

these secondary standards, but states may choose to 

adopt and enforce them.

Public Water Systems Must Meet 

National Drinking Water Standards

Drinking water standards apply to public water 

systems, which provide water to at least 15 

connections or 25 persons at least 60 days out of 

the year (most cities and towns, schools, businesses, 

campgrounds, and shopping malls are served by 

public water systems).

Private Wells

The 10 percent of Americans 

whose water comes from private 

wells (individual wells serving 

fewer than 25 persons) are not 

required to be protected by these 

federal standards. People with 

private wells are responsible 

for making sure that their own 

drinking water is safe. Some 

states do set standards for private 

wells, so well owners should 

check their state requirements. 

US EPA recommends testing 

your water once per year to 

see if it meets federal and state 

standards. Call the Safe Drinking 

Water Hotline at 1-800-426-

4791 or see the Safewater home 

page at www.epa.gov/ safewate r/

p rivatewell s to find out how to get 

a list of certified testing labs in 

your state. 

Bottled Water

Bottled water is regulated 

by the U.S. Food and Drug 

Administration as a food product, 

and is required to meet standards 

equivalent to those US EPA sets 

for tap water.

Steps in Drinking Water 

Standard Setting:

US EPA uses the following steps 

to set enforceable, health-based drinking water 

standards.

Determine whether a contaminant should be regulated 

based on peer-reviewed science, including data on: 

how often the contaminant occurs in the environment; 

how humans are exposed to it; the health effects of 

exposure, (particularly to vulnerable subpopulations).

Set a Maximum Contaminant Level Goal (MCLG) (the 

level of a contaminant in drinking water below which 

SAFE DRINKING WATER ACT 1974 - 2004 PROTECT OUR HEALTH FROM SOURCE TO TAP
there is no known or expected health risk. MCLGs 

allow for a margin of safety). These goals take into 

account the risks of exposure for certain sensitive 

populations, such as infants, the elderly, and persons 

with compromised immune systems. These goals 

are not enforceable levels because they do not take 

available technology into consideration, and therefore 

are sometimes set at levels which public water systems 

cannot meet.

Propose an enforceable standard in the form of a 

Maximum Contaminant Level (MCL) (the maximum 

amount of a contaminant allowed in water delivered 

to a user of any public water system) or a Treatment 

Technique (TT) (required procedure or level of 

technological performance set when there is no 

reliable method to measure a contaminant at very low 

levels). MCLs are set as close to MCLGs as feasible, 

considering available technology and cost. Examples 

of rules requiring treatment techniques are the Surface 

Water Treatment Rule (requires disinfection and 

filtration) and the Lead and Copper Rule (requires 

optimized corrosion control). Water samples that 

contain lead or copper exceeding the action level 

trigger additional treatment or other requirements 

that a water system must follow. Required testing 

(monitoring) schedules are part of the enforceable 

standard.

After determining a proposed MCL or TT that is as 

close to the MCLG as possible based on affordable 

technology, US EPA must complete an economic 

analysis to determine whether the benefits of that 

standard justify the costs. If not, US EPA may adjust 

the MCL for a particular class or group of systems to 

a level that “maximizes health risk reduction benefits 

at a cost that is justified by the benefits.” US EPA may 

not adjust the MCL if the benefits justify the costs to 

large systems and small systems that are unlikely to 

receive variances.

US EPA sets an enforceable MCL or TT. After 

considering comments on the proposed standard and 

other relevant information, US EPA makes final an 

enforceable Maximum Contaminant Level or Treatment 

Technique, including required testing and reporting 

schedules.

States are authorized to grant variances from 

standards for systems serving up to 3,300 people 

if the systems cannot afford to comply with a rule 

(through treatment, an alternative source of water, 

or other restructuring) and the systems install EPA 

approved variance technology. States can grant 

variances to systems serving 3,301 - 10,000 people 

with US EPA approval. SDWA does not allow small 

systems to have variances for microbial contaminants. 

Under certain circumstances exemptions from 

standards may be granted to allow extra time to seek 

other compliance options or financial assistance. After 

the exemption period expires, the public water system 

must be in compliance. The terms of variances and 

exemptions must ensure no unreasonable risk to public 

health. 

Determining Whether Standards Are 

Needed for Other Contaminants - the 

Contaminant Candidate List

The 1996 Amendments to SDWA requires that every 

5 years US EPA establish a list of contaminants which 

are known or anticipated to occur in public water 

systems and may require future regluations under 

SDWA. The list is developed with significant input from 

the scientific community and other interested parties. 

After establishing this contaminant candidate list, 

US EPA identifies contaminants which are priorities 

for additional research and data gathering. US EPA 

uses this information to determine whether or not a 

regulation is appropriate and this process is repeated 

for each list, every 5 years.

In order to support this decision-making, US EPA 

has also established a National Contaminant 

Occurrence Database (NCOD), which stores data on 

the occurrence of both regulated and unregulated 

contaminants. US EPA is also required to list and 

develop regulations for monitoring certain unregulated 

contaminants. These monitoring data will provide the 

basis for identifying contaminants that may be placed 

on future Contaminant Candidate Lists and support 

the US EPA Administrator’s decisions to regulate 

contaminants in the future.

Health Effects

Adverse health effects from contaminants that may 

occur in drinking water include acute effects that may 

immediately impact health and chronic effects that 

may occur if contaminants are ingested at unsafe 

levels over many years.

Drinking water that meets US EPA’s health-based 

standards is generally safe. People who are not 

healthy as a result of illness, age, or weakened 

immune systems, are more likely to be at risk from 

certain contaminants that may be found in drinking 

water. Infants and very young children are also 

more susceptible to some contaminants. Individuals 

concerned about their particular situations should 

consult their health care providers.

For More Information

To learn more about dcurrent drinking water 

standards, information on potential health effects of 

specific contaminants, and guidance to persons with 

severely compromised immune systems call the Safe 

Drinking Water Hotline at 1-800-426-4791 or visit the 

safewater web site at www.epa.gov/ safewate r.

Office of Water (4606) www.epa.gov/safewater EPA 816-F-04-037 June 2004